For years, Aleppo city has been on the receiving end of sporadic attacks from all sides: the armed Syrian opposition, the regime and its supporting militias, and Russia's air force. But a recent Assad army push to seize the rebels' supply line into the city was the most significant assault there in a long time. The military operation broke the Eid truce Assad himself had announced, setting off a race for control of the strategic road. Dozens of civilians died in ensuing clashes.

It is not news that Damascus, alongside Moscow, is trying to protect its interests on the northern border with Turkey. By seizing the Castello road Assad most probably has these interests in mind, as opposed to beating rebels, whether Islamist armed factions or jihadis like Jabhat al-Nusra, al-Qaeda's Syrian affiliate.

Possession of this vital road into Syria's second-largest citycould change the balance of power in talks when the sides meet again in Geneva. More importantly, however, it points to the regime following a 'long-game' policy, dividing the land, cutting the supply route, and besieging the area to weaken the armed opposition. The move will make it difficult for rebel groups to continue smuggling in weapons via Turkey, something that has long vexed Ankara. Recent overtures from Turkey to Damascusindicate the Erdogan government appreciates this policy shift.

Aleppo city has been divided in two since 2012.

Castello road connects Aleppo city with its suburbs, now battlefields mostly empty of residents, where different groups are in control. As such, the road is highly prized. The Syrian military controls the north, ISIS and the military hold parts of the east, Jabhat al-Nusra and other armed factions control the west, and Assad's army and the Turkestan Islamic Party (TIP) hold the south. Since the start of the war, there has been pressure on rebels to move from cities to suburbs to avoid the regime targeting civilians.

Assad has adapted the regime's policy against the armed opposition, as the latest Aleppo developments show. Locals, mostly in the city, have been allying themselves with extremist and jihadi groups, including Jabhat al-Nusra. This has strengthened the latter's presence in the area. According to the representative of one Aleppo's opposition factions, who preferred to remain nameless, "locals are allying with Jabhat al-Nusra because their fighters are on the ground and among them." He added: "People are ready to ally with the devil to get rid of the regime, especially after cutting off the Castello road. By doing so, the regime will leave people with no access to food, medicine, or any basics." There is reportedly little on-the-ground presence of moderate religious factions belonging to the Free Syrian Army, and backed by the US and Turkey, in the area. The vacuum is being filled by Islamist extremists like Jabhat al-Nusra and TIP.

Cutting the Aleppo supply road will leave people with no access to food.

Aleppo city has been divided in two since 2012. The west, home to two million, is under regime control. The east, with 300,000 residents, is in rebel hands. With the Castello road cut off by Assad, the rebel-held part of Aleppo will be isolated from the rest of Syria for the first time since military operations kicked off there four years ago. With no supplies and no entry route for back-up rebel forces, this will weaken opposition activity in one of the key arenas of Syria's conflict.

Currently, two main armed opposition groups operate in Aleppo. The first is mostly backed by Saudi Arabia and Turkey. It includes factions like Jaish al-Islam and the Fatah Halab operations room, both of which were involved in the recent clashes over the Castello road. These groups are often described as Islamist, though Jaish al-Islam's spokesperson, Islam Alloush, insists otherwise.

"We are not Islamists, we are Muslims," he says. "We fight religious extreme groups like Jabhat al-Nusra and ISIS ..... We consider ourselves a faction of the Free Syrian Army." The second comprises jihadi and Salafi-jihadi groups like ISIS and the Jaish al-Fatah coalition, which counts Jabhat al-Nusra among its ranks.

Though perhaps as many as 30 per cent of Jabhat al-Nusra fighters are not Syrians, they have bonded with local communities and see themselves as Syrian rebels fighting Assad – as well as rivals like ISIS. Jabhat al-Nusra gives security to Aleppo locals, who are mostly conservative Muslims. With some overlap in their religious beliefs, and little other assistance in sight, many locals see the al-Qaeda affiliate as a help, not an extremist hindrance.

Meanwhile, in the face of some opposition from the intelligence and military community, US Secretary of State Kerry is set to meet with Russia's Foreign Minister Lavrov to discuss cooperating with Assad's ally against extremists, like ISIS and Jabhat al-Nusra. If this goes ahead, the Moscow-Washington alliance would target Islamist extremist factions in Aleppo, and rightly so. But this would leave the door open for Assad to continue taking aim at armed opposition groups he deems 'terrorists,' devastating the opposition to his regime. Even more 'moderate,' US-backed groups would be at risk.